Semiconductor device

ABSTRACT

A semiconductor device includes a first circuit board on which a first switching element and a first diode connected in inverse parallel are mounted, a second circuit board on which a second switching element and a second diode connected in inverse parallel are mounted, a printed circuit board disposed opposite the first circuit board and the second circuit board, and a plurality of conductive posts which electrically connect the first switching element, the second switching element, the first diode, the second diode, the first circuit board, or the second circuit board and metal layers of the printed circuit board. The first switching element and the second switching element are connected in anti-series to form a bidirectional switch.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of International Application PCT/JP2015/060743 filed on Apr. 6, 2015 which designated the U.S., which claims priority to Japanese Patent Application No. 2014-082651, filed on Apr. 14, 2014, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The embodiments discussed herein relate to a semiconductor device.

2. Background of the Related Art

Highly efficient and low-noise power converters are developed for power conditioners for photovoltaic power generation, motor controllers for electric vehicles, and the like. The power converters include inverter units formed by combining semiconductor devices each including semiconductor chips.

Insulated gate bipolar transistors (IGBT), power metal-oxide-semiconductor field-effect transistors (MOSFET), and free wheeling diodes (FWD) are used as semiconductor chips included in semiconductor devices.

FIG. 11 is a sectional view which illustrates an example of the structure of a conventional semiconductor device.

A semiconductor device 100 illustrated in FIG. 11 includes two semiconductor chips 101 and 102. The semiconductor device 100 includes an insulating substrate 103. The insulating substrate 103 includes a ceramic board 103 a, a circuit board 103 b stuck on a front (upper surface in FIG. 11) of the ceramic board 103 a, and a metal board 103 c stuck on a back (under surface in FIG. 11) of the ceramic board 103 a.

The semiconductor chips 101 and 102 are joined to the circuit board 103 b by the use of solder 104 and a plurality of external terminals 105 are joined to the circuit board 103 b by the use of the solder 104.

Furthermore, a heat radiation base plate 107 is joined to the back of the metal board 103 c by the use of solder 108.

The semiconductor chips 101 and 102 are electrically connected by a bonding wire 109 and the semiconductor chip 102 and the circuit board 103 b are electrically connected by the bonding wire 109.

Furthermore, the base plate 107, the insulating substrate 103, and the semiconductor chips 101 and 102 are housed in a box-shaped resin case 110 having an open bottom. Furthermore, resin is injected into the resin case 110 and is cured. By doing so, the internal components are sealed.

An inverter unit is formed by combining a plurality of semiconductor devices each of which is similar to the above semiconductor device. It is suggested that at this time the plurality of semiconductor devices are connected by connecting their external terminals by the use of plate-shaped bus bars (see, for example, International Publication Pamphlet No. WO2013/146212).

By the way, with the conventional semiconductor device 100 wiring is performed by the use of thin bonding wires. This makes it difficult to reduce the wiring inductance in the semiconductor device 100. As a result, it is impossible to accommodate high-speed switching.

In addition, with the conventional technique described in, for example, International Publication Pamphlet No. WO2013/146212, plate-shaped bus bars are used for connecting a plurality of semiconductor devices. This reduces the wiring inductance among the semiconductor devices. However, there are various demands for the shapes of packages of actual semiconductor devices. As a result, wiring routing performed by the use of bus bars often becomes complex. Furthermore, usually a bus bar becomes thinner with a reduction in the size of semiconductor devices. In many cases, this leads to an increase in inductance.

SUMMARY OF THE INVENTION

According to one aspect, there is provided a semiconductor device including: a first switching element and a second switching element; a first diode and a second diode; a first circuit board on which the first switching element and the first diode are mounted; a second circuit board on which the second switching element and the second diode are mounted; a printed circuit board disposed opposite the first circuit board and the second circuit board and including metal layers; and a plurality of conductive posts which electrically connect the first switching element, the second switching element, the first diode, the second diode, the first circuit board, or the second circuit board and the metal layers of the printed circuit board, wherein a bidirectional switch is formed by connecting the first switching element and the first diode in inverse parallel; connecting the second switching element and the second diode in inverse parallel; and connecting the first switching element and the second switching element in anti-series via the plurality of conductive posts and, the metal layers, and the first circuit board or the second circuit board.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the basic structure of a three-level inverter unit to which a semiconductor device according to a first embodiment is applied;

FIG. 2 is a circuit diagram which illustrates an example of the structure of a three-level inverter;

FIG. 3 is a central vertical sectional view of the semiconductor device according to the first embodiment;

FIGS. 4A to 4C illustrate examples of a wiring pattern of the semiconductor device;

FIG. 5 is a perspective view which illustrates the appearance of the semiconductor device;

FIGS. 6A and 6B illustrate the forms of the use of the semiconductor device according to the first embodiment;

FIG. 7 is a circuit diagram which illustrates an example of the structure of a three-level inverter unit to which a semiconductor device according to a second embodiment is applied;

FIGS. 8A to 8C illustrate examples of a wiring pattern of the semiconductor device which forms the intermediate arm block illustrated in FIG. 7;

FIG. 9 is a circuit diagram which illustrates an example of the structure of a three-level inverter unit to which a semiconductor device according to a third embodiment is applied;

FIG. 10 is a circuit diagram which illustrates an example of the structure of a three-level inverter unit to which a semiconductor device according to a fourth embodiment is applied; and

FIG. 11 is a sectional view which illustrates an example of the structure of a conventional semiconductor device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will now be described in detail with reference to the drawings. A plurality of embodiments may be combined, if possible.

First Embodiment

FIG. 1 illustrates the basic structure of a three-level inverter unit to which a semiconductor device according to a first embodiment is applied. FIG. 2 is a circuit diagram which illustrates an example of the structure of a three-level inverter.

As illustrated in FIG. 1, a three-level inverter unit to which a semiconductor device according to a first embodiment is applied includes a direct-current power supply 1, a conversion section 2, and a filter section 3.

The conversion section 2 includes a capacitor Ca, a capacitor Cb, an inverter 4, and an intermediate arm block 5. One terminal of the capacitor Ca is connected to the positive electrode terminal P of the direct-current power supply 1 and the other terminal of the capacitor Ca is connected to a terminal of the capacitor Cb. Furthermore, the other terminal of the capacitor Cb is connected to the negative electrode terminal N of the direct-current power supply 1. The inverter 4 is connected in parallel with a circuit including the capacitor Ca and the capacitor Cb connected in series. The inverter 4 includes transistors Q1 and Q2 and diodes D01 and D02. The transistor Q1 and the diode D01 are connected in inverse parallel and make up the upper arm of the inverter 4. In addition, the transistor Q2 and the diode D02 are connected in inverse parallel and make up the lower arm of the inverter 4. In the present specification, the term “inverse parallel” is given its ordinary meaning and refers to elements configured to allow current flow in opposite directions. For example, where the diode D01 is configured to allow current flow from a first end to a second end, and the transistor Q1 is configured to allow current flow from a first end, such as a collector, to a second end, such as an emitter, the first end of the diode D01 is connected to the second end of the transistor Q01, and the second end of the diode D01 is connected to the first end of the transistor Q1. Furthermore, the upper arm and the lower arm are connected in series to form the inverter 4. In the example of FIG. 1, n-channel MOSFETs are used as the transistors Q1 and Q2. An intermediate arm block 5 is disposed between an intermediate potential point M between the capacitors Ca and Cb and an intermediate connection point U between the transistors Q1 and Q2. The intermediate arm block 5 is a bidirectional switch formed of semiconductor elements.

The filter section 3 connected to the conversion section 2 includes a coil L and a capacitor C. One end of the coil L is connected to the intermediate connection point U between the transistors Q1 and Q2 and the other end of the coil L is connected to one terminal of the capacitor C.

This three-level inverter unit always clamps voltage applied to the transistors Q1 and Q2 of the inverter 4 at half of voltage E of the direct-current power supply 1. As a result, an output waveform of the inverter 4 is a pulse width modulation (PWM) pulse obtained by combining ±E/2 and ±E with a zero point as a center. Therefore, a waveform generated by the three-level inverter unit is close to a sine wave compared with an output waveform of an ordinary two-level inverter unit. Furthermore, the filter section 3 used for making an output waveform a sine wave becomes smaller in size. In addition, the width of fluctuations in voltage at the time of the switching operation of the transistors Q1 and Q2 is half of that of a two-level inverter unit. As a result, switching loss or switching noise of the transistors Q1 and Q2 is reduced and efficiency in switching operation is improved.

A semiconductor device according to a first embodiment is applied to the intermediate arm block 5 of the above three-level inverter unit. As illustrated in FIG. 2, the intermediate arm block 5 according to a first embodiment includes transistors Q11 and Q12, which are IGBTs, and diodes D11 and D12.

The emitter, collector, auxiliary emitter, and gate of the transistor Q11 are connected to a terminal E1, a terminal C1/C2, a terminal E1 s, and a terminal G1 respectively. The anode and cathode of the diode D11 are connected to the terminal E1 and the terminal C1/C2 respectively. That is to say, the transistor Q11 and the diode D11 are connected in inverse parallel.

The emitter, collector, auxiliary emitter, and gate of the transistor Q12 are connected to a terminal E2, a terminal C1/C2, a terminal E2 s, and a terminal G2 respectively. The anode and cathode of the diode D12 are connected to the terminal E2 and the terminal C1/C2 respectively. That is to say, the transistor Q12 and the diode D12 are connected in inverse parallel.

The terminals C1/C2 are electrically connected inside the intermediate arm block 5. That is to say, all of the collector of the transistor Q11, the collector of the transistor Q12, the cathode of the diode D11, and the cathode of the diode D12 are connected to the terminals C1/C2. The transistors Q11 and Q12 are connected in this way in anti-series. In the present specification and claims, the term “anti-series” is given its ordinary meaning, which is two elements connected in series arranged in such a way as to permit current flow in opposite directions through a circuit. For example, as illustrated in FIG. 2, the collector of the transistor Q11 is connected to the collector of the transistor Q12 at terminal C1/C2.

The terminal E1 of the intermediate arm block 5 is connected to the intermediate potential point M which is a connection point common to the capacitors Ca and Cb, and the terminal E2 of the intermediate arm block 5 is connected to the intermediate connection point U which is a connection point common to the transistors Q1 and Q2. The terminals C1/C2 are not connected to an external circuit and are used for checking internal wiring, the characteristics of elements, and the like at production time.

The transistor Q11 is switched from an off (non-conducting) state to an on (conducting) state by applying determined voltage between the terminal G1 and the terminal E1 s. The transistor Q12 is also switched from an off state to an on state by applying determined voltage between the terminal G2 and the terminal E2 s.

When both of the transistors Q11 and Q12 are in an off state, an off state arises between the terminal E1 and the terminal E2.

Furthermore, when the transistor Q11 is in an on state and the transistor Q12 is in an off state, a circuit including the diode D12 and the transistor Q11 connected in series is in an on state. Therefore, the intermediate arm block 5 passes current in the direction of the terminal E2 to the terminal E1.

In addition, when the transistor Q11 is in an off state and the transistor Q12 is in an on state, a circuit including the diode D11 and the transistor Q12 connected in series is in an on state. Therefore, the intermediate arm block 5 passes current in the direction of the terminal E1 to the terminal E2.

As has been described, the intermediate arm block 5 has the above structure. As a result, the intermediate arm block 5 passes current in both directions by putting one of the transistors Q11 and Q12 into an on state and putting the other into an off state. That is to say, the intermediate arm block 5 has the function of a bidirectional switch.

Next, the concrete structure of a semiconductor device for realizing the intermediate arm block 5 having the above circuit structure will be described by the use of FIGS. 3 through 6.

FIG. 3 is a central vertical sectional view of the semiconductor device according to the first embodiment. FIGS. 4A to 4C illustrate examples of a wiring pattern of the semiconductor device. FIG. 4A illustrates a wiring pattern of a circuit board. FIG. 4B illustrates a wiring pattern on an upper surface of a printed circuit board. FIG. 4C illustrates a wiring pattern on an under surface of the printed circuit board. For ease of understanding, FIG. 4C illustrates a wiring pattern seen by turning over the printed circuit board (that is to say, wiring pattern seen through the upper surface). FIG. 5 is a perspective view which illustrates the appearance of the semiconductor device. FIGS. 6A and 6B illustrate the forms of the use of the semiconductor device according to the first embodiment.

A semiconductor device 10 includes a first switching element 14, a second switching element 16, a first diode 15, a second diode 17, a first circuit board 12 a, a second circuit board 12 b, a printed circuit board 18, and conductive posts 19 and 20. The semiconductor device 10 further includes third circuit boards 12 c, 12 d, 12 e, 12 f, 12 g, 12 h, 12 i, and 12 j and external terminals 21 a, 21 b, 22 a, 22 b, 23, 24, and 25. In the following, all of the above third circuit boards may collectively be referred to as the third circuit boards 12 c through 12 j.

As illustrated in FIGS. 3 and 4A, the semiconductor device 10 includes a first insulating substrate 11A and a second insulating substrate 11B disposed side by side in a horizontal direction. Each of the first insulating substrate 11A and the second insulating substrate 11B includes a ceramic board made of alumina, aluminum nitride, silicon nitride, or the like having good heat transferability, a circuit board disposed on its upper surface, and a metal board disposed on its under surface.

In addition, the first circuit board 12 a is disposed on the upper surface of the first insulating substrate 11A and a metal board 13 having the same thickness is disposed on the under surface of the first insulating substrate 11A. Furthermore, the second circuit board 12 b is disposed on the upper surface of the second insulating substrate 11B and a metal board 13 having the same thickness is disposed on the under surface of the second insulating substrate 11B. Moreover, the third circuit boards 12 c through 12 j are disposed on the upper surfaces of the first insulating substrate 11A and the second insulating substrate 11B. The first circuit board 12 a, the second circuit board 12 b, and the third circuit boards 12 c through 12 j are made of, for example, a copper plate greater than or equal to 0.5 mm thick and smaller than or equal to 1.5 mm thick.

The first switching element 14 and the first diode 15 are mounted on the first circuit board 12 a. Furthermore, the second switching element 16 and the second diode 17 are mounted on the second circuit board 12 b. The first switching element 14 and the first diode 15 correspond to the transistor Q11 and the diode D11, respectively, illustrated in FIG. 2. In addition, the second switching element 16 and the second diode 17 correspond to the transistor Q12 and the diode D12, respectively, illustrated in FIG. 2. Moreover, the first switching element 14, the first diode 15, the second switching element 16, and the second diode 17 are mounted separately over the two insulating substrates. If the two insulating substrates are integrally formed, thermal stress causes the insulating substrate to deform significantly. As a result, the insulating substrate or resin may crack or a circuit board or resin may peel off the insulating substrate. In this embodiment, on the other hand, the two insulating substrates are used. This improves reliability.

The printed circuit board 18 is disposed over and opposite the first circuit board 12 a and the second circuit board 12 b at a determined distance from them. A metal layer having a wiring pattern illustrated in FIG. 4B is formed on the upper surface of the printed circuit board 18 and a metal layer having a wiring pattern illustrated in FIG. 4C is formed on the under surface of the printed circuit board 18.

A determined metal layer of the printed circuit board 18 and the first circuit board 12 a, the second circuit board 12 b, or the third circuit boards 12 c through 12 j are electrically connected via a cylindrical conductive post 19. Furthermore, a determined metal layer of the printed circuit board 18 and the first switching element 14, the first diode 15, the second switching element 16, or the second diode 17 are electrically connected via a cylindrical conductive post 20. In addition, the external terminals 21 a, 21 b, 22 a, 22 b, 23, 24, and 25 are connected electrically and mechanically to the first circuit board 12 a and the third circuit boards 12 c through 12 j. These components are connected by the use of a conductive joining material such as solder or a sintered metal material.

The first circuit board 12 a, the second circuit board 12 b, the first switching element 14, the first diode 15, the second switching element 16, the second diode 17, the conductive posts 19 and 20, and the printed circuit board 18 are covered with resin such as thermosetting epoxy resin. As a result, the semiconductor device 10 illustrated in FIG. 5 is formed. By using resin 40, the semiconductor device 10 has an almost cuboid shape. The positions of the external terminals 21 a and 21 b disposed are symmetrical with respect to a center line which extends in the longitudinal direction. Similarly, the positions of the external terminals 22 a and 22 b disposed are symmetrical with respect to the center line which extends in the longitudinal direction. The positions of the external terminals 23 disposed are symmetrical with respect to the center line which extends in the longitudinal direction. The positions of the external terminals 24 disposed are symmetrical with respect to the center line which extends in the longitudinal direction. The positions of the external terminals 25 disposed are symmetrical with respect to the center line which extends in the longitudinal direction.

Electrical connection of the semiconductor device 10 described above will now be described with reference to FIG. 2.

As illustrated in FIG. 4A, the first insulating substrate 11A and the second insulating substrate 11B are disposed side by side in the longitudinal direction of the semiconductor device 10.

The first circuit board 12 a and the third circuit boards 12 c, 12 d, 12 e, and 12 f are disposed on the upper surface of the first insulating substrate 11A. The first switching element 14 and the first diode 15 are mounted on the first circuit board 12 a and the two external terminals 23 are connected to the first circuit board 12 a. The external terminals 21 a, 21 b, 22 a, and 22 b are connected to the third circuit boards 12 c, 12 d, 12 e, and 12 f respectively.

The second circuit board 12 b and the third circuit boards 12 g, 12 h, 12 i, and 12 j are disposed on the upper surface of the second insulating substrate 11B. The second switching element 16 and the second diode 17 are mounted on the second circuit board 12 b. The two external terminals 24 are connected to the third circuit boards 12 g and 12 h respectively. The two external terminals 25 are connected to the third circuit boards 12 i and 12 j respectively.

The shape of each of the first circuit board 12 a and the second circuit board 12 b is symmetrical with respect to a center line 41 extending in a direction in which the first insulating substrate 11A and the second insulating substrate 11B are disposed side by side. In addition, the positions of the third circuit boards 12 c and 12 d disposed are symmetrical with respect to the center line 41. Similarly, the positions of the third circuit boards 12 e and 12 f disposed are symmetrical with respect to the center line 41. The positions of the third circuit boards 12 g and 12 h disposed are symmetrical with respect to the center line 41. The positions of the third circuit boards 12 i and 12 j disposed are symmetrical with respect to the center line 41. Furthermore, the switching element 14, the first diode 15, the second switching element 16, and the second diode 17 are disposed on the above center line 41.

Each of the first switching element 14 and the second switching element 16, which are IGBTs, has an emitter electrode and a gate electrode on its front and has a collector electrode on its back. Furthermore, the collector electrode of the first switching element 14 is connected electrically and mechanically to the first circuit board 12 a and the collector electrode of the second switching element 16 is connected electrically and mechanically to the second circuit board 12 b.

In addition, each of the first diode 15 and the second diode 17 has an anode electrode on its front and has a cathode electrode on its back. Moreover, the cathode electrode of the first diode 15 is connected electrically and mechanically to the second circuit board 12 b.

The first circuit board 12 a, the second circuit board 12 b, and the third circuit boards 12 c through 12 j have a plurality of connection points 12 k at which they are connected to the printed circuit board 18 via the conductive posts 19.

As illustrated in FIG. 4B, metal layers 18 a, 18 b, 18 c, 18 d, 18 e, and 18 f are disposed on the upper surface of the printed circuit board 18. The metal layers 18 a, 18 b, and 18 c are metal layers for a main circuit. The metal layers 18 d and 18 e are metal layers for a gate circuit. The metal layer 18 f is a metal layer for a terminal connection.

As illustrated in FIG. 4C, metal layers 18 g, 18 h, 18 i, 18 j, 18 k, and 18 l are disposed on the under surface of the printed circuit board 18. The metal layers 18 g, 18 h, and 18 i are metal layers for the main circuit. The metal layer 18 j is a metal layer for a terminal connection. The metal layers 18 k and 18 l are metal layers for an auxiliary emitter and are electrically connected to the metal layers 18 g and 18 i respectively.

A plurality of penetration holes 18 m are made in the printed circuit board 18. The positions of the plurality of penetration holes 18 m correspond to the positions of the plurality of connection points 12 k, the electrodes of the first switching element 14, the electrode of the first diode 15, the electrodes of the second switching element 16, and the electrode of the second diode 17. In addition, penetration holes 18 n whose positions correspond to positions at which the external terminals 21 a, 21 b, 22 a, 22 b, 23, 24, and 25 are connected are made in the printed circuit board 18.

The collector electrode of the first switching element 14 is connected via the first circuit board 12 a to the external terminals 23 (terminals C1/C2). The emitter electrode of the first switching element 14 is connected via the conductive post 20 to the metal layers 18 a and 18 g of the printed circuit board 18 first and is then connected via the conductive post 19 and the third circuit board 12 g (or the third circuit board 12 h) to the external terminal 24 (terminal E1). The gate electrode of the first switching element 14 is connected via the conductive post 20 to the metal layer 18 d first and is then connected via the conductive post 19 and the third circuit board 12 c to the external terminal 21 a (terminal G1). An auxiliary emitter electrode of the first switching element 14 is connected via the conductive post 20 to the metal layer 18 g first and is then connected via the metal layer 18 k, the conductive post 19, and the third circuit board 12 e to the external terminal 22 a (terminal E1 s).

The cathode electrode of the first diode 15 is connected via the first circuit board 12 a to the external terminals 23 (terminals C1/C2). The anode electrode of the first diode 15 is connected via the conductive post 20 to the metal layers 18 a and 18 g first and is then connected via the conductive post 19 and the third circuit board 12 g (or the third circuit board 12 h) to the external terminal 24 (terminal E1).

The collector electrode of the second switching element 16 is connected via the second circuit board 12 b and the conductive post 19 to the metal layers 18 b and 18 h first and is then connected via the conductive post 19 and the first circuit board 12 a to the external terminals 23 (terminals C1/C2). That is to say, the metal layers 18 b and 18 h function as a bridge which forms a current path of the collector between the first insulating substrate 11A and the second insulating substrate 11B separate from each other. The emitter electrode of the second switching element 16 is connected via the conductive post 20 to the metal layers 18 c and 18 i first and is then connected via the conductive post 19 and the third circuit board 12 i (or the third circuit board 12 j) to the external terminal 25 (terminal E2). The gate electrode of the second switching element 16 is connected via the conductive post 20 to the metal layer 18 e first and is then connected via the conductive post 19 and the third circuit board 12 d to the external terminal 21 b (terminal G2). An auxiliary emitter electrode of the second switching element 16 is connected via the conductive post 20 to the metal layer 18 i first and is then connected via the metal layer 18 l, the conductive post 19, and the third circuit board 12 f to the external terminal 22 b (terminal E2 s).

The cathode electrode of the second diode 17 is connected via the second circuit board 12 b and the conductive post 19 to the metal layers 18 b and 18 h first and is then connected via the conductive post 19 and the first circuit board 12 a to the external terminals 23 (terminals C1/C2). The anode electrode of the second diode 17 is connected via the conductive post 20 to the metal layers 18 c and 18 i first and is then connected via the conductive post 19 and the third circuit board 12 i (or the third circuit board 12 j) to the external terminal 25 (terminal E2).

Wiring inside the semiconductor device 10 having the above structure is formed of the printed circuit board 18 and the conductive posts 19 and 20. As a result, current paths are broad and short compared with the bonding wires used in the conventional semiconductor device 100. Therefore, the wiring inductance is significantly reduced. This means that a semiconductor device which accommodates high-speed switching is realized.

In addition, a plurality of semiconductor devices 10 can easily be connected in parallel in order to increase the current capacity of the intermediate arm block 5. FIG. 6A illustrates an example of the intermediate arm block 5 whose current capacity is increased by disposing two semiconductor devices 10 side by side and connecting them in parallel by the use of bus bars 26, 27, and 28. With the semiconductor device 10 according to the first embodiment the two external terminals 23 are disposed side by side in the lateral direction of the semiconductor device 10. Similarly, the two external terminals 24 are disposed side by side in the lateral direction of the semiconductor device 10 and the two external terminals 25 are disposed side by side in the lateral direction of the semiconductor device 10. As a result, even if a plurality of semiconductor devices 10 are connected in parallel, external terminals 23 are disposed straight. Similarly, external terminals 24 are disposed straight and external terminals 25 are disposed straight. Therefore, each of the bus bars 26, 27, and 28 provides the shortest straight wiring. This reduces not only the wiring inductance inside the semiconductor device but also the wiring inductance outside the semiconductor device 10. As a result, a large-current-capacity semiconductor device which accommodates high-speed switching is realized.

Furthermore, in the example of FIG. 6B, the inverter 4 and the intermediate arm block 5 illustrated in FIG. 2 are housed in packages of identical shape and a semiconductor device 4 a of the inverter 4 and the semiconductor device 10 of the intermediate arm block 5 are combined. It is assumed that with the semiconductor device 4 a of the inverter 4 external terminals are disposed in the order of gate terminals and auxiliary source terminals of the transistors Q1 and Q2, the positive electrode terminals P, the negative electrode terminals N, and the intermediate connection points U from the bottom of FIG. 6B.

The semiconductor device 4 a of the inverter 4 and the semiconductor device 10 of the intermediate arm block 5 are disposed side by side in the lateral direction of them and are connected by a bus bar 29 and a laminated bus bar 30.

The bus bar 29 connects the external terminals (terminals E2) of the semiconductor device 10 and the intermediate connection points U of the semiconductor device 4 a at the shortest distance. The laminated bus bar 30 is formed by laminating four metal conductor and insulating film sheets. The laminated bus bar 30 includes a bus bar 30 a connected to the terminals C1/C2, a bus bar 30 b connected to the positive electrode terminals P, a bus bar 30 c connected to the intermediate potential points M, and a bus bar 30 d connected to the negative electrode terminals N. The bus bar 30 a is connected to the external terminals 23 of the semiconductor device 10. The bus bar 30 b is connected to the positive electrode terminals P of the semiconductor device 4 a. The bus bar 30 c is connected to the external terminals 24 of the semiconductor device 10. The bus bar 30 d is connected to the negative electrode terminals N of the semiconductor device 4 a.

The semiconductor device 4 a of the inverter 4 and the semiconductor device 10 of the intermediate arm block 5 are connected in this way at the shortest distance by the bus bar 29 and the laminated bus bar 30. This reduces not only the wiring inductance inside the semiconductor device 4 a and the semiconductor device 10 but also the wiring inductance outside the semiconductor device 4 a and the semiconductor device 10. Furthermore, because the laminated bus bar 30 includes many layers is applied, the mutual inductance of external wiring between the semiconductor device 4 a and the semiconductor device 10 is also reduced. As a result, a three-level inverter unit which accommodates high-speed switching is provided.

In the first embodiment the example in which one first switching element 14, one first diode 15, one second switching element 16, and one second diode 17 are used is taken. However, plural first switching elements 14, plural first diodes 15, plural second switching elements 16, and plural second diodes 17 may be connected in parallel, depending on the magnitude of required current capacity.

Furthermore, the first switching element 14, the first diode 15, the second switching element 16, and the second diode 17 may be made of a silicon semiconductor or a wide-band-gap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), or diamond.

Second Embodiment

FIG. 7 is a circuit diagram which illustrates an example of the structure of a three-level inverter unit to which a semiconductor device according to a second embodiment is applied. FIGS. 8A to 8C illustrate examples of a wiring pattern of the semiconductor device which forms the intermediate arm block illustrated in FIG. 7. FIG. 8A illustrates a wiring pattern of a circuit board, FIG. 8B illustrates a wiring pattern on an upper surface of a printed circuit board, and FIG. 8C illustrates a wiring pattern on an under surface of the printed circuit board. For ease of understanding, FIG. 8C illustrates a wiring pattern seen by turning over the printed circuit board (that is to say, wiring pattern seen through the upper surface).

Components in the second embodiment which are the same as or equivalent to those illustrated in the first embodiment will be marked with the same numerals and detailed descriptions of them will be omitted.

Components used in an intermediate arm block 5 a which is a semiconductor device according to a second embodiment are the same as those used in the intermediate arm block 5 which is the semiconductor device according to the first embodiment. However, the intermediate arm block 5 a differs from the intermediate arm block 5 in circuit structure. That is to say, the collectors of the transistors Q11 and Q12 are connected in the intermediate arm block 5 which is the semiconductor device according to the first embodiment. On the other hand, emitters of transistors Q11 and Q12 are connected in the intermediate arm block 5 a which is a semiconductor device according to a second embodiment. Details will now be described.

The emitter, collector, auxiliary emitter, and gate of the transistor Q11 are connected to a terminal E1/E2, a terminal C1, a terminal E1 s, and a terminal G1 respectively. The anode and cathode of a diode D11 are connected to the terminal E1/E2 and the terminal C1 respectively. That is to say, the transistor Q11 and the diode D11 are connected in inverse parallel.

The emitter, collector, auxiliary emitter, and gate of the transistor Q12 are connected to a terminal E1/E2, a terminal C2, a terminal E2 s, and a terminal G2 respectively. The anode and cathode of a diode D12 are connected to the terminal E1/E2 and the terminal C2 respectively. That is to say, the transistor Q12 and the diode D12 are connected in inverse parallel.

The terminals E1/E2 are electrically connected inside the intermediate arm block 5 a. That is to say, all of the emitter of the transistor Q11, the emitter of the transistor Q12, the anode of the diode D11, and the anode of the diode D12 are connected to the terminals E1/E2. The transistors Q11 and Q12 are connected in this way in anti-series.

The terminal C1 of the intermediate arm block 5 a is connected to an intermediate potential point M which is a connection point common to capacitors Ca and Cb, and the terminal C2 of the intermediate arm block 5 a is connected to an intermediate connection point U which is a connection point common to transistors Q1 and Q2.

By adopting the above structure, the intermediate arm block 5 a passes current in both directions by putting one of the transistors Q11 and Q12 into an on state and putting the other into an off state. That is to say, the intermediate arm block 5 a has the function of a bidirectional switch. This is the same with the first embodiment.

With a semiconductor device (not illustrated) of the intermediate arm block 5 a terminals to which external terminals 23, 24, and 25 are connected are different from the terminals to which the external terminals 23, 24, and 25 are connected in the first embodiment. That is to say, the external terminals 23 are connected to the terminals E1/E2 common to the emitters of the transistors Q11 and Q12, the external terminals 24 are connected to the terminal C1 of the collector of the transistor Q11, and the external terminals 25 are connected to the terminal C2 of the collector of the transistor Q12.

The collector electrode of a first switching element 14 corresponding to the transistor Q11 is connected via a first circuit board 12 a and a conductive post 19 to metal layers 18 b and 18 h first and is then connected via a conductive post 19 and a third circuit board 12 i (or a third circuit board 12 j) to the external terminal 24 (terminal C1). The emitter electrode of the first switching element 14 is connected via a conductive post 20 to metal layers 18 a and 18 g first and is then connected via a conductive post 19 and a third circuit board 12 g (or a third circuit board 12 h) to the external terminal 23 (terminal E1/E2). The gate electrode of the first switching element 14 is connected via a conductive post 20 to a metal layer 18 d first and is then connected via a conductive post 19 and a third circuit board 12 c to an external terminal 21 a (terminal G1). The auxiliary emitter electrode of the first switching element 14 is connected via a conductive post 20 to the metal layer 18 g first and is then connected via the metal layer 18 g, a metal layer 18 k, a conductive post 19, and a third circuit board 12 e to an external terminal 22 a (terminal E1 s).

The cathode electrode of a first diode 15 corresponding to the diode D11 is connected via the first circuit board 12 a and the conductive post 19 to the metal layers 18 b and 18 h first and is then connected via the conductive post 19 and the third circuit board 12 i (or the third circuit board 12 j) to the external terminal 24 (terminal C1). The anode electrode of the first diode 15 is connected via the conductive post 20 to the metal layers 18 a and 18 g first and is then connected via the conductive post 19 and the third circuit board 12 g (or the third circuit board 12 h) to the external terminal 23 (terminal E1/E2).

The collector electrode of a second switching element 16 corresponding to the transistor Q12 is connected via a second circuit board 12 b to the external terminal 25 (terminal C2). The emitter electrode of the second switching element 16 is connected via a conductive post 20 to a metal layer 18 i first and is then connected via the metal layer 18 g, the conductive post 19, and the third circuit board 12 g (or the third circuit board 12 h) to the external terminal 23 (terminal E1/E2). The gate electrode of the second switching element 16 is connected via a conductive post 20 to a metal layer 18 e first and is then connected via a conductive post 19 and a third circuit board 12 d to an external terminal 21 b (terminal G2). The auxiliary emitter electrode of the second switching element 16 is connected via a conductive post 20 to the metal layer 18 i first and is then connected via a metal layer 18 l, a conductive post 19, and a third circuit board 12 f to an external terminal 22 b (terminal E2 s).

The cathode electrode of a second diode 17 corresponding to the diode D12 is connected via the second circuit board 12 b to the external terminal 25 (terminal C2). The anode electrode of the second diode 17 is connected via a conductive post 20 to the metal layer 18 i first and is then connected via the metal layer 18 g, the conductive post 19, and the third circuit board 12 g (or the third circuit board 12 h) to the external terminal 23 (terminal E1/E2).

Wiring inside the semiconductor device having the above structure is formed of a printed circuit board 18 and the conductive posts 19 and 20. This is the same with the first embodiment. As a result, current paths are broad and short compared with the bonding wires used in the conventional semiconductor device 100. Therefore, the wiring inductance is significantly reduced. This means that a semiconductor device which accommodates high-speed switching is realized.

Third Embodiment

FIG. 9 is a circuit diagram which illustrates an example of the structure of a three-level inverter unit to which a semiconductor device according to a third embodiment is applied.

IGBTs are used as the transistors in the intermediate arm block 5 according to the first embodiment. However, power MOSFETs are used as transistors in an intermediate arm block 5 b which is a semiconductor device according to a third embodiment. That is to say, the intermediate arm block 5 b includes transistors Q21 and Q22, which are power MOSFETs, and diodes D21 and D22. Accordingly, components which are the same as or equivalent to those illustrated in the first embodiment will be marked with the same numerals in the following description and detailed descriptions of them will be omitted.

The source, drain, auxiliary source, and gate of the transistor Q21 are connected to a terminal S1, a terminal D1/D2, a terminal S1 s, and a terminal G1 respectively. The anode and cathode of the diode D21 are connected to the terminal S1 and the terminal D1/D2 respectively. That is to say, the transistor Q21 and the diode D21 are connected in inverse parallel.

The source, drain, auxiliary source, and gate of the transistor Q22 are connected to a terminal S2, a terminal D1/D2, a terminal S2 s, and a terminal G2 respectively. The anode and cathode of the diode D22 are connected to the terminal S2 and the terminal D1/D2 respectively. That is to say, the transistor Q22 and the diode D22 are connected in inverse parallel.

The terminals D1/D2 are electrically connected inside the intermediate arm block 5 b. That is to say, all of the drain of the transistor Q21, the drain of the transistor Q22, the cathode of the diode D21, and the cathode of the diode D22 are connected to the terminals D1/D2. The transistors Q21 and Q22 are connected in this way in anti-series.

The terminal S1 of the intermediate arm block 5 b is connected to an intermediate potential point M which is a connection point common to capacitors Ca and Cb, and the terminal S2 of the intermediate arm block 5 b is connected to an intermediate connection point U which is a connection point common to transistors Q1 and Q2.

As a result, the intermediate arm block 5 b functions as a bidirectional switch by putting one of the transistors Q21 and Q22 into an on state and putting the other into an off state.

The intermediate arm block 5 b has the same structure as the intermediate arm block 5 according to the first embodiment has. Accordingly, the same first circuit board 12 a, second circuit board 12 b, and printed circuit board 18 that are illustrated in the first embodiment may be used.

Fourth Embodiment

FIG. 10 is a circuit diagram which illustrates an example of the structure of a three-level inverter unit to which a semiconductor device according to a fourth embodiment is applied.

IGBTs are used as the transistors in the intermediate arm block 5 a according to the second embodiment. However, power MOSFETs are used as transistors in an intermediate arm block 5 c which is a semiconductor device according to a fourth embodiment. That is to say, the intermediate arm block 5 c includes transistors Q21 and Q22, which are power MOSFETs, and diodes D21 and D22. Accordingly, components which are the same as or equivalent to those illustrated in the second embodiment will be marked with the same numerals in the following description and detailed descriptions of them will be omitted.

The source, drain, auxiliary source, and gate of the transistor Q21 are connected to a terminal S1/S2, a terminal D1, a terminal S1 s, and a terminal G1 respectively. The anode and cathode of the diode D21 are connected to the terminal S1/S2 and the terminal D1 respectively. That is to say, the transistor Q21 and the diode D21 are connected in inverse parallel.

The source, drain, auxiliary source, and gate of the transistor Q22 are connected to a terminal S1/S2, a terminal D2, a terminal S2 s, and a terminal G2 respectively. The anode and cathode of the diode D22 are connected to the terminal S1/S2 and the terminal D2 respectively. That is to say, the transistor Q22 and the diode D22 are connected in inverse parallel.

The terminals S1/S2 are electrically connected inside the intermediate arm block 5 c. That is to say, all of the source of the transistor Q21, the source of the transistor Q22, the anode of the diode D21, and the anode of the diode D22 are connected to the terminals S1/S2. The transistors Q21 and Q22 are connected in this way in anti-series.

The terminal D1 of the intermediate arm block 5 c is connected to an intermediate potential point M which is a connection point common to capacitors Ca and Cb, and the terminal D2 of the intermediate arm block 5 c is connected to an intermediate connection point U which is a connection point common to transistors Q1 and Q2.

As a result, the intermediate arm block 5 c functions as a bidirectional switch by putting one of the transistors Q21 and Q22 into an on state and putting the other into an off state.

The intermediate arm block 5 c has the same structure as the intermediate arm block 5 a according to the second embodiment has. Accordingly, the same first circuit board 12 a, second circuit board 12 b, and printed circuit board 18 that are illustrated in the first embodiment may be used.

In the present specification and claims, the term “conductive post” refers to a column of conductive material that is formed to be free-standing. As described above, after manufacture or after positioning of the post within the electrical circuit, the post and other components may be covered by resin. However, in embodiments of the invention, the post is not formed by filling an opening in the resin with conductive material.

With the semiconductor device having the above structure, the wiring inductance in the semiconductor device is reduced and the external wiring inductance between the semiconductor device and another semiconductor device is reduced.

All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A semiconductor device comprising: a first switching element and a second switching element; a first diode and a second diode; a first circuit board on which the first switching element and the first diode are mounted, the first switching element and the first diode mounted on a first surface of the first circuit board; a second circuit board on which the second switching element and the second diode are mounted, the second switching element and the second diode mounted on a first surface of the second circuit board; a printed circuit board disposed opposite the first circuit board and the second circuit board and including metal layers; and a plurality of conductive posts which electrically connect two or more of the first switching element, the second switching element, the first diode, the second diode, the first circuit board, and the second circuit board with two or more of the metal layers of the printed circuit board, wherein the first circuit board and the second circuit board are arranged horizontally, such that the first surface of the first circuit board and the first surface of the second circuit board each face a same surface of the printed circuit board, wherein the first and second switching elements are configured to form a bidirectional switch, the bidirectional switch comprising: the first switching element connected to the first diode in inverse parallel; the second switching element connected to the second diode in inverse parallel; and the first switching element connected to the second switching element in anti-series via the plurality of conductive posts, the two or more of the metal layers, and at least one of the first circuit board and the second circuit board, wherein the first switching element includes a first terminal on a rear surface of the first switching element facing the first surface of the first circuit board, the first terminal for allowing current to flow into the first switching element when the first switching element is turned on the first diode includes a cathode on a rear surface of the first diode facing the first surface of the first circuit board, the first terminal of the first switching element is electrically connected to the cathode of the first diode via a conductive layer of the first circuit board, and the first terminal of the first switching element is electrically connected to a cathode of the second diode via at least one conductive post, among the plurality of conductive posts, and the printed circuit board, such that when the first switching element is turned on, current flows from the second diode, through the at least one conductive post, to the first terminal of the first switching element.
 2. The semiconductor device according to claim 1, further comprising: a plurality of external terminals; and a plurality of third circuit boards to which one or more of the plurality of external terminals and one or more of the plurality of conductive posts are connected.
 3. The semiconductor device according to claim 2, wherein: a shape of each of the first circuit board and the second circuit board is symmetrical with respect to a center line extending in a direction in which the first circuit board and the second circuit board are disposed side by side; the plurality of third circuit boards are disposed in positions symmetrical with respect to the center line; and the plurality of external terminals, which are equal in potential to the first switching element, the second switching element, the first diode, or the second diode, are connected to the plurality of third circuit boards.
 4. The semiconductor device according to claim 2, wherein: the first circuit board is included in a first insulating substrate; and the second circuit board is included in a second insulating substrate.
 5. The semiconductor device according to claim 4, wherein: a metal board is included on a surface of the first insulating substrate opposite to a surface on which the first circuit board is included; and a metal board is included on a surface of the second insulating substrate opposite to a surface on which the second circuit board is included.
 6. The semiconductor device according to claim 4, wherein: the first circuit board, the second circuit board, the first switching element, the second switching element, the first diode, the second diode, the plurality of conductive posts, and the printed circuit board are covered with resin of cuboid shape; and the plurality of external terminals protrude in a same direction from the resin of cuboid shape and are disposed in a longitudinal direction of the resin of cuboid shape.
 7. The semiconductor device according to claim 1, wherein the first switching element and the second switching element are insulated gate bipolar transistors (IGBTs).
 8. The semiconductor device according to claim 7, wherein a collector of the IGBT mounted on the first circuit board and a collector of the IGBT mounted on the second circuit board are electrically connected via a first conductive post, from among the plurality of conductive posts, extending between the first circuit board and the printed circuit board, and a second conductive post, from among the plurality of conductive posts, extending between the second circuit board and the printed circuit board.
 9. The semiconductor device according to claim 7, wherein an emitter of the IGBT mounted on the first circuit board and an emitter of the IGBT mounted on the second circuit board are electrically connected via a first conductive post, from among the plurality of conductive posts, extending between the first circuit board and the printed circuit board, and a second conductive post, from among the plurality of conductive posts, extending between the second circuit board and the printed circuit board.
 10. The semiconductor device according to claim 1, wherein the first switching element and the second switching element are power metal oxide semiconductor field effect transistors (MOSFETs).
 11. The semiconductor device according to claim 10, wherein a drain of the power MOSFET mounted on the first circuit board and a drain of the power MOSFET mounted on the second circuit board are electrically connected via a first conductive post, from among the plurality of conductive posts, extending between the first circuit board and the printed circuit board, and a second conductive post, from among the plurality of conductive posts, extending between the second circuit board and the printed circuit board.
 12. The semiconductor device according to claim 10, wherein a source of the power MOSFET mounted on the first circuit board and a source of the power MOSFET mounted on the second circuit board are electrically connected via a first conductive post, from among the plurality of conductive posts, extending between the first circuit board and the printed circuit board, and a second conductive post, from among the plurality of conductive posts, extending between the second circuit board and the printed circuit board.
 13. A semiconductor device comprising: a first switching element and a second switching element; a first diode and a second diode; a first circuit board on which the first switching element and the first diode are mounted, the first switching element and the first diode mounted on a first surface of the first circuit board; a second circuit board on which the second switching element and the second diode are mounted, the second switching element and the second diode mounted on a first surface of the second circuit board; a printed circuit board disposed opposite the first circuit board and the second circuit board and including metal layers; a plurality of posts connecting the printed circuit board with the first and second circuit boards; a first external terminal; a second external terminal; and a third external terminal, wherein: the first and second switching elements are configured to form a bidirectional switch, the bidirectional switch comprising: the first switching element and the first diode connected in inverse parallel, the second switching element and the second diode connected in inverse parallel, and the first switching element and the second switching element connected in anti-series; the first external terminal is connected to an emitter electrode of the first switching element; the second external terminal is connected to an emitter electrode of the second switching element; and the third external terminal is connected to a collector electrode of the first switching element and a collector electrode of the second switching element, wherein the first circuit board and the second circuit board are arranged horizontally, such that the first surface of the first circuit board and the first surface of the second circuit board each face a same surface of the printed circuit board, wherein the first switching element includes a first terminal on a rear surface of the first switching element facing the first surface of the first circuit board, the first terminal for allowing current to flow into the first switching element when the first switching element is turned on, the first diode includes a cathode on a rear surface of the first diode facing the first surface of the first circuit board, the first terminal of the first switching element is electrically connected to the cathode of the first diode via a conductive layer of the first circuit board, and the first terminal of the first switching element is electrically connected to a cathode of the second diode via at least one post, from among the plurality of posts, and the printed circuit board, such that when the first switching element is turned on, current flows from the second diode, through the at least one post, to the first terminal of the first switching element.
 14. The semiconductor device according to claim 13, wherein the plurality of posts electrically connect two or more of the first switching element, the second switching element, the first diode, the second diode, the first circuit board, and the second circuit board with two or more of the metal layers of the printed circuit board, and wherein the first switching element and the second switching element are connected in anti-series via the plurality of posts and the two or more of the metal layers.
 15. A semiconductor device comprising: a first switching element and a second switching element; a first diode and a second diode; a first circuit board on which the first switching element and the first diode are mounted, the first switching element and the first diode mounted on a first surface of the first circuit board; a second circuit board on which the second switching element and the second diode are mounted, the second switching element and the second diode mounted on a first surface of the second circuit board; a printed circuit board disposed opposite the first circuit board and the second circuit board and including metal layers; a plurality of posts connecting the printed circuit board with the first and second circuit boards; a first external terminal; a second external terminal; and a third external terminal, wherein: the first switching element and the second switching element are configured to form a bidirectional switch, the bidirectional switch comprising: the first switching element connected to the first diode in inverse parallel, the second switching element connected to the second diode in inverse parallel, and the first switching element connected to the second switching element in anti-series; the first external terminal is connected to a collector electrode of the first switching element; the second external terminal is connected to a collector electrode of the second switching element; and the third external terminal is connected to an emitter electrode of the first switching element and an emitter electrode of the second switching element, wherein the first circuit board and the second circuit board are arranged horizontally, such that the first surface of the first circuit board and the first surface of the second circuit board each face a same surface of the printed circuit board, wherein the first switching element includes a first terminal on a rear surface of the first switching element facing the first surface of the first circuit board, for allowing current to flow into the first switching element when the first switching element is turned on, the first diode includes a cathode on a rear surface of the first diode facing the first surface of the first circuit board, the first terminal of the first switching element is electrically connected to the cathode of the first diode via a conductive layer of the first circuit board, and the first terminal of the first switching element is electrically connected to a cathode of the second diode via at least one post, from among the plurality of posts, and the printed circuit board, such that when the first switching element is turned on, current flows from the second diode, through the at least one post, to the first terminal of the first switching element.
 16. The semiconductor device according to claim 15, wherein the plurality of posts electrically connect two or more of the first switching element, the second switching element, the first diode, the second diode, the first circuit board, and the second circuit board with two or more of the metal layers of the printed circuit board, and wherein the first switching element and the second switching element are connected in anti-series via the plurality of posts and the two or more of the metal layers. 